1. Field of the Invention
The present invention relates to a combustion-engined setting tool for driving fastening elements such as, e.g., nails, bolts, pins, in a constructional components and which includes a combustion chamber, means arranged in the combustion chamber for generating turbulence of an oxidant-fuel mixture filling the combustion chamber, an ignition unit for igniting the oxidant-fuel mixture, and drive means for a least temporarily driving the turbulence generating means.
2. Description of the Prior Art
In the setting tools described above, a portion of the liquid gas or another vaporable fuel, which is mixed with an oxidant, e.g., environmental air, is combusted in the tool combustion chamber. In order to obtain as high as possible drive-in energy from the combustion process, it is important that the combustion of the gas or gas mixture takes place under turbulent flow conditions. Only a turbulent combustion permits to obtain a necessary drive-in energy from the combustion process, producing a sufficiently rapid pressure increase in the combustion chamber for accelerating the setting piston to a degree necessary for driving a fastening element in. With a laminar combustion, the combustion process and the resulting pressure increase take place so slow that only a fraction of the required mechanical energy can be obtained from the combustion process.
European Patent EP-0 544471B1 discloses a combustion-engined setting tool having a combustion chamber for combusting a mixture of air and fuel gas and in which ventilator means is provided in the combustion chamber for generating turbulence therein. The ventilator means is driven by an electric motor which is supplied with electrical energy from a battery. The ventilator means is actuated by the head switch of the setting tool when the setting tool is pressed against a constructional component. The ignition unit is actuated for igniting the air-fuel mixture in the combustion chamber when an actuation switch is actuated, while the head switch is still closed.
The drawback of the setting tool of the European Patent consist in complicated and costly electronics which actuates and controls the ventilator means and which also actuates ignition. A further drawback consists in that several accumulators are needed, which increases the tool weight.
German Publication DE 199 62 711 A1 discloses a combustion-engined setting tool in which a separation plate with through-openings is arranged in the combustion chamber, dividing the combustion chamber in two chambers. An adjustment device is used for changing the distance between the separation plate and a rear wall that axially limits the combustion chamber, whereby the volumes of the forechamber and the main chamber change. In the forechamber, a first portion of the air-fuel mixture is ignited, with the flame jets penetrating into the main chamber through the openings in the separation plate, creating turbulence in the main chamber and igniting the air-fuel mixture therein.
The drawback of the tool disclosed in DE 199 62 711 A1 consists in that the combustion process is sensible to the environmental conditions such as, e.g., temperature, scavenging ratio of the combustion chamber, or the environmental pressure. This results from the fact that the turbulence is generated as a result of the combustion process itself, i.e., when the combustion in the forechamber is poor, then the combustion in the main chamber is even worse.
German Publication DE 102 26 878 A1 discloses a combustion-engined setting tool in which, as in the previously described case, the turbulence is generated by a perforated separation plate that remains static before and during the ignition process. After the combustion process ends, the separation plate and the rear wall are displaced in a direction toward the piston guide, so that the combustion chamber completely collapses. After the combustion chamber has collapsed, another, non-perforated plate is displaced as a result of application thereto a spring-biasing force from a location at the rear end of the setting tool remote from the piston guide up to the rear wall in order to scavenge the space before this plate with fresh air.
Here, likewise, the drawback consists in that the combustion process is sensible to the fluctuation of the environmental conditions such as, e.g., temperature, scavenging ratio of the combustion chamber, or the environmental pressure.
The object of the present invention is to provide a setting tool of the type described above and in which the drawbacks of the known tools are eliminated.
Another object of the present invention is to provide a setting tool of the type described above which would have a high energy efficiency.